Print hammer drive mechanism



NOW 1964 R. D. NELSON ETAL 3,155,033

PRINT HAMMER DRIVE MECHANISM 2 Sheets-Sheet 1 Filed May 29, 1961 INVENTOR. ROLAND D. NELSON DONALD K. REX

ATTORNEY NOV. 3, 1964 NELSON ETAL 3,155,033

PRINT HAMMER DRIVE MECHANISM Filed May 29, 1961 2 Sheets-Sheet 2 United States Patent 3,155,033 PRINT HAMlt IER DRIVE MECHANISM Roland B. Nelson and Donald K. Rex, San Jose, Calif.,

assignors to international Business Machines Corporation, New York, N.Y., a corporation of New York Filed May 29, 1961, Ser. No. 113,291 9 (Ilaims. (Cl. 101-?3) The present invention relates to a print hammer drive mechanism for a high speed printer and more particularly to an electromechanical drive mechanism for selecting, driving and resetting the hammers in such a printer.

In high speed printers it is common to use a horizontal type bar which is moved back and forth across the print medium in increments. The type bar generally consists of a fiexible, sheet metal comb with a character of type mounted on the distal end of each tooth or finger of the comb. A row of aligned print hammers extends across the printer, one hammer for each print position, and the type bar is driven incrementally between the hammers and the print medium. Printing of a given character is accomplished by striking a tooth or finger with a selected hammer, causing the finger to bend forward until the type face bears against the print medium. The type bar is so arranged that each different character successively passes each print position. The desired characters to be printed on any one line are stored in a memory bufier, one character storage for each print position. The particular print character on the type bar in each particular print position is read and com ared with the information stored in the memory. If a compare results, the hammer corresponding to that print position is fired to strike the type bar and print the desired character.

, Various type mechanical and electromechanical hammer drive mechanisms, such as cam, work-magnet, spring, etc., have been suggested for use in prior art printers. Each type drive mechanism, however, has a number of shortcomings which limit either the price or the performance of the printer. The cam type drive is complex and expensive, due to the large number of cams and the selection means required to prevent undesired hammers from firing. The work-magnet type drive is likewise complex and expensive, because of the heavy power requirements to operate the magnets and the circuitry required to overcome the effects of residual magnetism and induction in order to provide precise timing. The spring type drive is attractive from the standpoint of reliability and simplicity of design. However, such drives have heretofore utilized coil springs which were designed to remain in engagement with the hammers at all times. Accordingly, hammer restore and latch mechanisms have been bulky, since they have had to oppose the combined force of all the hammer drive springs.

The object of the present invention is to provide a canti lever spring drive mechanism for print hammers and one which is inexpensive, compact and reliable.

The shortcomings of the prior art hammer drive mechanisms are avoided in the present invention by provision of a cantilever spring drive which disengages after the print hammer has been fired. A leaf-type spring is provided for each hammer, the springs being mounted in cantilever fashion on a common spring bail. Cam-positioned reset mechanism is provided to stop the flight of each individual spring, to compress each fired spring, and to reset the springs en masse after the hammers have been restored to their cocked position.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawlugs.

Patented Nov. 3, 1964 FIG. 1 is an elevational view in schematic showing the drive mechanism of the present invention after the hammer has been fired;

FIG. 2 is an elevation view similar to FIG. 1 showing the drive mechanism in its reset position; and

FIG. 3 is a perspective view, partially in section, showing the arrangement of the various parts of the present invention.

Referring more particularly to FIGS. 1 and 3 of the drawings, a printer is shown as including a platen 10, a type bar 11, an array of hammers 12 and an array of holding magnets 13. A hammer return spring 14 and a hammer drive mechanism, shown generally at 15, are mounted adjacent each hammer for contact therewith. Each hammer includes a central body portion which is slotted as at to to receive a pivot rod 17. A flange 18 protrudes upwardly from the body portion and a firing arm 19 extends below the body portion.

The hammer firing mechanism 15 includes a cantilever leaf spring 21 for each hammer, each spring being mounted on a bail 22 which is pivotally suspended from a shaft 23 on arms 24 and 25. Each drive spring 21 is made up of a number of leaves 26 through 29 of progressively decreasing effective lengths. Leaf 27 is provided with an angularly protruding finger 31 at its distal end. The. drive mechanism includes a spring reset assembly made up of a spring stop bail 32 pivotally mounted on shaft 23 by means of arms 33 and 34. A plurality of pairs of cams 35 through 38 are keyed at intervals to a shaft 39, cam 35 being identical to cam 37 and cam 36 being similarly identical to cam 38. Cam followers $1 and 42 are carried by arms 24 and 25 in position to bear against cams 35 and 37, While cam followers 43 and 44 are carried by arms 33 and 34 in position to bear against cams 36 and 38. Cam followers 41 and 42 are kept in contact with earns 35 and 37 through the reaction of d-rivespring 21. Cam followers 43 and 44 are maintained in contact with cams 3'5 and 38 by tension springs 45and 46. As shown in FIG. 3, the opposite ends of shafts 23 and 39 are journaled in the printer frame 47. Hammer return springs 14 are likewise mounted on the frame, as are platen 1i] and pivot rod 17.

In the operation of the present invention, the upper end of each drive spring rests against the firing arm of ita corresponding print hammer, as shown in FIG. 2, and the spring flexure imparts a clockwise force to the print hammer. In the position shown, each holding magnet maintains its associated hammer against the force exerted by the drive spring. As the type bar moves along in front of the hammers from character position to character position, the correct hammers are released at each position by de-energizing the corresponding control magnets. This is accomplished by switching off the current through coils 48 to neutralize the holding action of the magnets. When a control magnet is ale-energized, the associated print hammer is accelerated in a clockwise direction by the drive spring. As the print hammer pivots, the tip of the drive spring slides off the lower tip of the firing arm and comes to rest against the spring stop bail, as shown in FIG. 1. The acceleration given to the hammer causes it to continue in its movement until it strikes the type bar and forces the type against the print medium on the platen. The hammer then rebounds away from the platen in a counterclockwise direction toward the holding magnet. As the hammer rebounds, the firing arm contacts finger 31 which provides a braking action to prevent the hammer from striking the holding magnet. The hammer return spring 14, bearing against the flange 18, acts against finger 31 to hold the hammer in position slightly spaced from both legs of the magnet. V

The array 'of hammers remains fixed laterally with respect to the platen and the print medium thereon. Each glances 3 hammer therefore corresponds to a particular character position on the print medium and need be driven only once during each line of print. Thus, at each position of the type bar, selected hammers are driven, after which the type bar moves to the next position and a different selection of print hammers is driven.

Upon completion of each line of print, the holding magnets are re-energized. The drive springs are all reset simultaneously then by the following action. The cam shaft 39 is rotated in a clockwise direction, causing the spring mounting bail 2 2 to move down and to the left and then causing the spring stop bail 32 to move down and to the right. The result is that the distal ends of the disengaged drive springs move down and to the right and pass beneath the lower tips of the firing arms. The return springs then return the hammers to the magnets and hold the hammers against the pivot rod and both pole faces. Further cam shaft rotation moves the spring mounting bail upward and to the right, causing the drive springs to move upward until contact is made with the firing arms of the hammers as shown in FIG. 2. Continued rotation of the cam shaft then returns the spring stop bail to its former position as shown in FIG. 1 and the printer is ready to print another line. The drive springs are then reset to their loaded position by a single rotation of the cam shaft after each line has been printed.

An advantage of the present invention is that the use of no-work magnets for holding the hammers requires far less power than that required by a work magnet used to drive the hammer. Another advantage is derived from disengaging the drive spring, since each hammer is then automatically returned to its starting position by a simple cantilever return spring.

By mounting both the spring stop bail and the spring mounting bail for pivotal motion about a common axis, both bails can be controlled by cams secured to a single motor driven cam shaft. This arrangement permits radial motion of the cam followers relative to the cams and avoids any complementary motion between the bails. The result is a simplified but rigid mechanical construction.

While the invention has been particularly shown and described with reference to a preferred embodiment therein, it will be understood by those skilled in the art that the foregoing and other changes in the form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. For use in a high speed printer which includes an array of aligned print hammers with one hammer for each print position of the printer, a hammer drive mechanism for firing each hammer individually, comprising: an elongated pivotally mounted bail; an array of parallel leaf springs mounted in cantilever fashion on the bail there being a spring for each hammer, each spring being positioned in line with and extending toward a hammer, the distal end of each spring adapted to overlap a portion of its associated hammer in its loaded position; and a spring reset assembly mounted adjacent the bail to stop each spring in its unloaded position, the assembly and the bail cooperating to reset the springs to their loaded position.

2. For use in a high speed printer which includes an array of aligned print hammers with one hammer for each print position of the printer, a hammer drive mechanism for firing each hammer individually, comprising: a spring mounting bail pivotally mounted on the printer and extending parallel to the hammer array; a plurality of leaf-type drive springs mounted in cantilever fashion on the spring mounting bail and extending toward the hammer array there being a drive spring for each hammer, the distal end of each drive spring adapted to overlap a portion of its associated hammer in its loaded position; and a drive spring stop bail pivotally mounted on the printer for movement toward and away from the spring mounting bail.

a fashion on the spring mounting bail and extending to-,

3. For use in a high speed printer which includes an array of aligned print hammer-s with one hammer for each print position of the printer, a hammer drive mechanism for firing each hammer individually, comprising: a spring mounting bail pivotally mounted on the printer and extending parallel to the hammer array; a plurality of leaf-type drive springs mounted in cantilever fashion on the spring mounting bail and extending toward the hammer array, the distal end of each drive spring adapted to overlap a portion of its associated hammer; a drive spring stop bail pivotally mounted coaxially with the spring mounting bail for movement towards and away from the hammer array; and a plurality of cams coaxially mounted in the printer adjacent the stop and spring mounting bails for positioning both bails.

4. For use in a high speed printer which includes an array of aligned print hammers with one hammer for each print position of the printer, a hammer drive mechanism comprising: a spring mounting bail pivotally mounted on the printer and extending parallel to the hammer array; a plurality of leaf-type drive springs mounted in cantilever fashion on the spring mounting bail, each drive spring being positioned in line with and extending toward a hammer, the distal end of each drive spring adapted to overlap a portion of its associated hammer in its loaded position; a pivotally mounted stop bail extending parallel to the spring mounting bail and spaced therefrom to limit movement of the drive springs in their unloaded condition, the stop bail and the spring mounting bail being mounted for pivotal movement about a common axis; and a plurality of coaxial cams mounted adjacent the bails in driving relation therewith.

5. The combination of a hammer drive mechanism and a high speed printer, comprising: an array of aligned hammers, one hammer for each print position of the printer, each hammer including a firing arm; a spring mounting bail; an array of drive springs mounted in cantilever fashion on the spring mounting bail and extending toward the hammer array, the distal end of each drive spring overlapping the firing arm of a hammer in its loaded position; and a stop bail positioned adjacent the firing arms and spaced therefrom to limit movement of the drive springs in their. unloaded condition, the stop bail and the spring mounting bail being mounted for movement toward and away from each other about a com mon axis.

6. The combination of a hammer drive mechanism and a high speed printer, comprising: an array of aligned hammers, one hammer for each print position of the printer, each hammer including a firing arm; a spring mounting bail extending the length of the hammer array; an array of parallel drive springs mounted in cantilever ward the hammer array, the distal end of each drive spring overlapping the firing arm of a hammer in its loaded position; a stop bail extending the length of the hammer array, the stop bail being positioned adjacent the firing arms and spaced therefrom to limit movement of the drive springs in their unloaded condition, the stop bail and the spring mounting bail being pivotally mounted about a common axis; and a plurality of coaxial cams mounted on a rotatable cam shaft adjacent the bails, the cams being drivingly connected to the bails to impart pivotal motion thereto.

7. In a high speed printer, the combination of an array of aligned print hammers;

selectively releasable means for holding the print hammers in cocked position; support means mounted adjacent the hammer array for pivotal movement toward and away from the hammers; individual hammer drive means mounted on the support means, the drive means bearing against the hammers in cocked position and being clear of the hammers in fired position; a

5 5 hammer drive reset means pivotally mounted for movedrive springs mounted in cantilever fashion on the supment toward and away from the support means, the port means, reset means and support means cooperating to recock the drive means and reinstate driving contact between References fited in the file of this patent the drive means and hammers; and 5 UNETED STATES PATENTS means for controlling the motion of the reset means and uppgrt means OIIIlSbY 4, 8. The combination recited in claim 7 including a plu- 1,926,891 Bryce p 1933 rality of cams mounted adjacent the reset means and the 9 B y t a 1, 1933 support means and in driving relation therewith to im- 10 2,227,143 Kutsen Dec. 31, 1940 part pivotal motion thereto. 2,325,966 Mills Aug. 3, 1943 9. The combination recited in claim 7 in which the 2,737,883 Crawford M r, 13, 1956 hammer drive means includes a plurality of leaf-type 

1. FOR USE IN A HIGH SPEED PRINTER WHICH INCLUDES AN ARRAY OF ALIGNED PRINT HAMMERS WITH ONE HAMMER FOR EACH PRINT POSITION OF THE PRINTER, A HAMMER DRIVE MECHANISM FOR FIRING EACH HAMMER INDIVIDUALLY, COMPRISING: AN ELONGATED PIVOTALLY MOUNTED BAIL; AN ARRAY OF PARALLEL LEAF SPRINGS MOUNTED IN CANTILEVER FASHION ON THE BAIL THERE BEING A SPRING FOR EACH HAMMER, EACH SPRING BEING POSITIONED IN LINE WITH AND EXTENDING TOWARD A HAMMER, THE DISTAL END OF EACH SPRING ADAPTED TO OVERLAP A PORTION OF ITS ASSOCIATED HAMMER IN ITS LOADED POSITION; AND A SPRING RESET ASSEMBLY MOUNTED ADJACENT THE BAIL TO STOP EACH 